Implementation of OPC UA Communication Traffic Control for Analog Values in an Automation Device with Embedded OPC UA Servers

Abstract

Integration of management information systems is crucial to optimizing internal and external processes in enterprises' environments. One of the technologies sup-porting this integration is OPC UA. An embedded automation device OPC UA server can transmit either dead-band tested analog attributes or all changes of ana-log attributes to OPC UA clients. Typically OPC UA server to OPC UA client data transmission is based on subscriptions. Subscription interval, sampling interval, and dead-band are usually controlled by OPC UA clients [1]. It is, however, desirable that OPC UA data traffic is controlled by automation de-vice control programs and the embedded OPC UA servers and not by OPC UA clients as specified in the norm. This is because the OPC UA server is the limiting component in the client sever communication scheme. Floating-point attributes in an automation device have small changes all the time, but in real-world plants, analog attributes do not necessarily have to be frequently communicated to OPC UA clients on small changes. In addition to an attribute dead-band test, changes in some attributes can safely be blocked a minimum time since the last attribute update before a new value is transmitted to the UA clients. Analog attributes can also be cyclically transmitted to OPC UA clients with a low frequency to ensure that they receive the exact attribute value after a set maximum time. This paper demonstrates an implementation of this communication scheme by using a device function block to control traffic between an OPC UA server and OPC UA clients for analog attributes.